Polypropylene has various industrial applications, particularly it is widely applied for materials used in automobiles and electronic products, etc. with various usages. For more expanded applications of polypropylene, an improvement in rigidity which may be led by an increase in the degree of crystallinity is further required as well as a wide molecular weight distribution so as to have improved processability. In order to obtain such properties in polypropylene, it is needed for a solid catalyst for preparing the same to be designed to have high stereoregularity and wide molecular weight distribution.
For polymerization of olefins such as propylene or the like, a solid catalyst comprising magnesium, titanium, an internal electron donor and halogen as essential elements is known in this field of art, and methods for polymerizing or copolymerizing olefins have been proposed many. However, such methods are not satisfying in terms of obtaining polymers having high stereoregularity with a high production yield, and thus needed to be improved in the above aspect.
In order to reduce the production cost by increasing the polymerization activity and improve physical properties of the resulted polymers by improving the catalyst performance such as stereoregularity, it is generally known in this field of art to use diester of aromatic dicarboxylic acid as an internal electron donor and related patent applications have been filed many, for examples, U.S. Pat. No. 4,562,173, U.S. Pat. No. 4,981,930, Korean Patent No. 0072844 and the like. The above patents describe a method for preparing a catalyst showing high activity and stereoregularity by using aromatic dialkyldiesters or aromatic monoalkylmonoesters. However, those aromatic carboxyl ester compounds used in the prior arts of the above-mentioned patents are known as endocrine disruptors which have adverse effect even at very small amount, on human health such as causing problems in fertility or reproductive functions in human, growth disorders, deformation and cancers as well as ecosystem. In this regard, there have been needs for the use of an eco-friendly internal electron donor in preparation of polypropylene which is generally used as a food packaging material. Further, the methods according to the above-mentioned patents cannot provide high stereoregular polymers with a high yield to the satisfying degree and thus further improvements in the methods are needed.
EP 0362705B1 proposes a method for preparing a catalyst using 1,3-diether compounds as an internal electron donor. However, this method is need to be further improved in terms of activity and stereoregularity, and has a relatively small molecular weight distribution thereby not being suitable for the preparation of polypropylene which requires wide molecular weight distribution.
Korean Patent No. 0572616 discloses a preparation method for a catalyst using a non-aromatic compound containing both ketone and ether groups, however stereoregularity and molecular weight distribution still need to be significantly improved.